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Evolution of reef and atoll margin carbonates, upper Eocene through lower Miocene, Enewetak, Marshall Islands

Conference ·
OSTI ID:6083344
;

Two wells drilled along the margin of Enewetak Atoll penetrated approximately 1,000 m of upper eocene, Oligocene, and lower Miocene carbonates. STrontium isotope stratigraphy indicates relatively continuous deposition of carbonate from 40 Ma to 20 Ma. Depositional environments show a gradual basinward progradation of facies with slope carbonates passing upward into fore-reef, reef, back-reef, and lagoonal carbonates. Slope strata contain wackestones and packstones with submarine-cemented lithoclasts, coral, coralline algae fragments, benthic rotaline forams, planktonic forams, and echinoderm fragments. Fore-reef strata are dominantly packstones and boundstones containing large pieces of coral, abundant benthic forams, coralline algae fragments, stromatoporoids(.), and minor planktonic forams. Reef and near-reef sediments include coralgal boundstones and grainstones with abundant benthic forams. Halimeda and miliolid forams are common in lagoonward parts of the back reef. Sponge borings, geopetal structures, and fractures are common in reef and fore-reef strata. Lagoonal strata are wackestones and packstones with common mollusks, coral, coralline algae, and benthic forams (rotaline and miliolid). Diagenesis has extensively altered strata near the atoll margin. Aragonite dissolution and calcite cements (radiaxial and cloudy prismatic are abundant in fore-reef, reef, and some back-reef strata). Petrographic and geochemical data indicate arogonite dissolution and calcite cementation in seawater at burial depths of 100 to 300 m. Dolomite occurs in slope and deeply buried reefal carbonates.

OSTI ID:
6083344
Report Number(s):
CONF-880301-
Country of Publication:
United States
Language:
English

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Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
03 NATURAL GAS
030200 -- Natural Gas-- Reserves
Geology
& Exploration
AGE ESTIMATION
ALKALINE EARTH METAL COMPOUNDS
CALCITE
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATE ROCKS
CARBONATES
CEMENTING
CENOZOIC ERA
CHEMISTRY
CONTINENTAL MARGIN
DEPOSITION
DOLOMITE
EOCENE EPOCH
EXPLORATION
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
GEOLOGY
ISLANDS
ISOTOPE DATING
MAGNESIUM CARBONATES
MAGNESIUM COMPOUNDS
MARSHALL ISLANDS
MICRONESIA
MINERAL RESOURCES
MINERALS
MIOCENE EPOCH
NATURAL GAS DEPOSITS
OCEANIA
OXYGEN COMPOUNDS
PETROGRAPHY
PETROLEUM DEPOSITS
PETROLEUM GEOLOGY
REEFS
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
STRATIGRAPHY
TERTIARY PERIOD